The present invention relates to telephone call processing, more particularly to the translation of a dialed telephone number for routing a tall to the appropriate switching facility tat serves the called station.
The public switched telephone network (PSTN) comprises multiple switching offices that require signaling between the offices for processing telephone calls. Signaling functions include transmitting routing and destination information transmitting alerting messages such as to indicate the arrival of an incoming call, and transmitting supervisor information, e.g. relating to line status. Signaling between offices can use xe2x80x98in-bandxe2x80x99 transport or xe2x80x98out-of-bandxe2x80x99 transport.
In-band signaling utilizes the same channel that carries the communications of the parties. In a voice telephone system one of the common forms of in-band signaling between offices utilizes multi-frequency signaling over voice trunk circuits. The same voice trunk circuits also carry the actual voice traffic between switching offices. In-band signaling, however, tends to be relatively slow and ties up full voice channels during the signaling operations. In telephone call processing, a substantial percentage of all calls go unanswered because the destination station is busy. For in-band signaling, the trunk to the end office switching system serving the destination is set-up and maintained for the duration of signaling until that office informs the originating office of the busy line condition. In-band signaling thus adds to congestion in the voice channels of the telephone network. In-band signaling also is susceptible to fraud by hackers who have developed devices which mimic in-band signaling.
Out-of-band signaling has evolved to mitigate the problems of in-band signaling. Out-of-band signaling utilizes separate channels, and in many cases separate switching elements, thereby alleviating communication channel congestion. As out-of-band signaling utilizes its own signal formats and protocols, unconstrained by protocols and formats utilized for the actual communication, it is considerably faster than in-band signaling. All end user communications remain in-band, making it virtually impossible for an end user hacker to simulate signaling messages which ride on an out-of-band channel or network.
Out of band signaling telephone networks include data links in one or more packet switching systems, known collectively as the Common Channel Signaling (CCS) or Common Channel Interoffice Signaling (CCIS) system. This system typically uses signaling system 7 (SS7) protocol. An SS7 compliant CCIS network comprises data switching systems designated Signal Transfer Points (STPs) and data links between the STPs and various telephone switching offices of the network. In advanced versions of the telephone network including high level control nodes, identified as Service Control Points (SCPs) or Integrated Service Control Points (ISCPs , the CCIS network also includes data links connecting the high level control nodes to one or more of the STPs.
Each central office in the PSTN is assigned an area code (NPA) and exchange code (NXX) in accordance with the North American Number Plan (NANP). From the range of ten digit telephone numbers available with an NPA-NXX code, the subscriber at any particular station is assigned a ten-digit telephone number (NPA-NXX-XXXX). Central office switching systems typically include a programmable digital switch with CCIS communications capabilities. One example of such a switch is a 5ESS type switch manufactured by ATandT. Other vendors, such as Northern Telecom and Siemens, manufacture comparable digital switches.
The STPs are program controlled packet data switching systems that facilitate routing of calls. In call routing operation, an STP will receive a packet data message from another node of the network, for example from an end office switching system. The STP analyzes point code information in the packet and routes the packet according to a translation table stored within the STP. This translation table is static. Any packet having a particular point code is output on a port going to the next CCIS signaling node specified by translation of that point code. The point code information received by an STP may be generated by a call originating office switch, such as the aforementioned 5ESS type switch. Each switching office facility contains translation tables by which dialed digits received from a calling station is converted to the appropriate point code. It can be appreciated that the complexity and xe2x80x9cintelligencexe2x80x9d capability required of central office switches continue to increase as switch functionality expands.
The advent of open competition among service providers of local telephone services, which have their own independent switching facilities integrated into the public switched telephone network, imposes even greater demands on the network switches. Telephone subscribers who change their local service providers must be afforded the opportunity to retain their previously assigned ten-digit telephone number so that change in service can occur in a seamless manner from the user""s perspective. The scope of telephone number portability may be extended further, for example, to permit a user to keep the same telephone number at the same or different location, while terminating service from one provider in favor of a new service provider, and moving from plain old telephone service (POTS) to integrated digital services network (ISDN). While an actual change of connections at the same or different premises by a technician will permit customer off-hook to draw dial tone for calling out, the ability to receive incoming calls is not so easily effected. The network must be capable of routing calls dialed to the same subscriber""s number through the changed facilities. Conventional call processing methods would require that the appropriate routing identification information for any active telephone number be accessible to the originating switch associated with a calling party of a ported number call. The xe2x80x9cportingxe2x80x9d of an active telephone number from one central office switching facility to another renders obsolete the NXX translation previously stored for that number at each switch in the network. Whether updated information will be stored at each switch or at a remote location in the network, the involvement and complexity of central office switches will be increased if call processing will occur according to current methodology. Current practice would require a change at each network switch each time new ported number service for any subscriber is to take effect.
Such change would involve either ah update in the storage in each switch of the changed translation or, at least, the setting of an appropriate trigger to obtain the information from a remote database location. Reference is made to commonly assigned copending U.S. patent application Ser. No. 09/053,678, filed Apr. 2, 1998, entitled LOCAL NUMBER PORTABILITY SERVICE SAVER for a more detailed description of aspects of telephone number portability.
Aside from the disadvantages associated with increased switch complexity, the need to make changes at each network switch whenever a new ported telephone number subscription takes place, imposes significant burden on the ability to maintain seamless service. Additional complexities are involved in the provision of accurate billing records, which are normally determined by rate tables for specific central offices that are associated with NXX exchange codes.
The present invention avoids the drawbacks and disadvantages described above, in part by relocating telephone number translations and other data, such as class of service, that heretofore resided in central offices to one or more locations remote from the switches. Such locations may contain Integrated Service Control Points (ISCPs), or processing systems of like capacity, that are accessible through the SS7 network to the central office switches that serve calling subscribers.
An advantage of the present invention is that translation tables that relate exchange codes to point codes, as well as triggers for routing to ported numbers, need not be set individually in each central office. Information for each new service in accordance with the invention can be loaded only into a single, or relatively few, centrally located databases rather than at each switch.
In another aspect of the invention, the central office equipment identifier for each ten digit number, such as the line equipment number (LEN), can be stored in the remote database. Consequently, network management can be handled by the ISCP or the like device for both line control and trunk control.
A further advantage of the present invention is that off-hook triggers can be set uniformly at all central offices for all originating calls. Once set, no further trigger updating is required each time an individual change in service for a subscriber line occurs thereafter. All information necessary for processing any call may be accessed routinely by each switch via the SS7 network from the remote location. The need for various complex trigger mechanisms, such as terminating triggers, and continual updating thereof, will be eliminated. Each network switch thus can be simplified. With substantially all the data and xe2x80x9cintelligencexe2x80x9d removed from the switch, the central office can thus take on the appearance of a station address, per se.
Another advantageous aspect of the present invention is that billing rate tables may be assigned individually to phone numbers, rather than NXXs in serving central offices. Thus billing records can be developed for all calls at the location removed from the central office by application of the rate tables and accumulation of call time at the removed location.